The present application relates to systems, devices and methods for maskless material removal from substrates using charged particle beams; and more particularly to directly removing material from precise locations as defined in a design layout database using multiple, matched charged particle beams, with the assistance of gas and/or photon injection, and/or of gas and/or photon process control, metrology and endpoint detection.
Note that the points discussed below may reflect the hindsight gained from the disclosed inventions, and are not necessarily admitted to be prior art.
FIG. 2A shows an example of a wafer 200 being scanned by multiple charged particle beams 204 emitted by respective miniature electrostatically-deflected beam columns 206. Individual columns 206 are able to target a portion 202 of the substrate surface with their respectively emitted beams 204.
FIG. 2B shows an example of a wafer 200. Example die 208 size and column 206 center-to-center spacing 210 (column separation) are shown. A regular grid of columns 206 (columns 206 are shown via their center positions, represented here as plusses) can use different spacing 210 in different (generally, orthogonal) directions. Die 208 size and column separation 210 are not required to (and generally, will not) correspond. Column separation 210 generally corresponds to the “writing area” of corresponding columns 206. A column's 206 “writing area” is defined as the substrate area 202 targetable by a charged particle beam 204 emitted from the column 206, taking into account stage movement.
The multiple column 206 array comprises miniature (small enough to fit multiple columns in an array) charged particle beam columns 206 arranged in a regular grid. For example, column 206 arrays with center-to-center column spacing 210 of 30 mm×30 mm have been implemented, though other column spacings 210 (e.g., 24 mm×33 mm) can also be used.
A stripe is the portion of the wafer 200 surface that a charged particle beam can target while the stage is moving predominantly in a single direction, i.e., before the stage moves laterally and switches predominant directions to give the beam access to a different stripe. A “frame” is defined herein as the portion of the wafer surface that a beam can target at a given time, corresponding to the main-field deflection area at that time, as designated by the design layout database. A frame is typically designated to be rectangular, for convenience (e.g., to tile the writing area); and smaller than the furthest extent to which the beam can be deflected (e.g., to preserve beam targeting accuracy).
“1-D” refers to 1-D gridded design rule. In a 1-D layout, optical pattern design is restricted to lines running in a single direction, with features perpendicular to the 1-D optical design formed in a complementary lithography step known as “cutting”. The complementary step can be performed using a charged particle beam lithography tool comprising an array of columns 206—for example, electrostatically-controlled miniature electron beam columns 206. A 1-D layout is separated in the design layout database into a “line pattern” and a “cut pattern”. The design layout database contains the information needed by lithography tools to pattern one or more layers on a substrate. A line pattern generally comprises an array of unidirectional lines. Cut patterns generally comprise line-cuts and holes.
Generally, line patterns are written by an optical lithography system, which can be followed by other process steps to increase the density of lines on the substrate. Cut patterns are written by a complementary (generally higher-resolution) process, such as electron beam lithography. Use of electron beam lithography for this complementary process is also called complementary e-beam lithography, or CEBL. The combination of the line-forming process followed by line-cuts written with CEBL to pattern a substrate layer is called complementary lithography.
FIG. 2C shows an example of a prior art process for removing material from a substrate surface.
Typically, as shown in FIG. 2C, a design layout database is used to designate where substrate surface material should be removed 212 (e.g., to form new pattern or repair previously-formed pattern). One or more optical masks are fabricated based on the design layout database 214 using a mask making tool 216. Fabrication of an optical mask typically takes weeks and costs millions of dollars at advanced process nodes.
A hard mask is blanket deposited on the substrate surface 218 by a deposition tool 220, and a photoresist layer is blanket deposited on the substrate surface 222 by a resist deposition tool 224.
“Blanket” deposition and etch generally refers to deposition and etch on the entire surface of the substrate.
“Resist” refers herein to a class of materials used in substrate lithography. When a resist is deposited on a substrate and exposed to an energy source corresponding to the type of resist (e.g., photons for a photoresist) in a chosen pattern, its chemical properties change such that when the resist is developed (in ways similar to developing a photographic film), a portion of the resist corresponding to a positive or negative image of the pattern (depending on the type of resist) will remain, allowing the pattern to be expressed in the material underlying the resist, e.g., using etch steps.
The photoresist is then exposed using the optical mask(s) 226 by an optical lithography tool 228. The exposed portion of the substrate (as designated by the optical mask(s)) is removed 230 using a resist developing tool 232, and the resulting patterned resist layer is inspected for defects and process control metrology (After Develop Inspection (ADI) and metrology) 234 by an inspection tool 236. Yield-reducing errors can be reduced by other tools, adding additional steps, and potentially additional defects.
The hard mask is then blanket etched through the pattern expressed in the resist layer 238, by an etch tool 240, to express (substantially) the same pattern in the hard mask layer. The resist layer is then removed 242 by a resist removal tool 244, and the material underlying the hard mask is blanket etched through the pattern expressed in the hard mask 246, using an etch tool 248 (e.g., a reactive-ion etch or ion milling tool, generally the same type of tool as etch tool 240), to express (substantially) the same pattern in the underlying material. One of ordinary skill in the arts of charged particle beam material removal will understand that other and/or additional steps can be used in a conventional material removal process.
Ti represents the amount of time added by a corresponding process step. Yi represents the yield impact of a corresponding process step (one minus probability of introducing one or more yield-reducing defects). Where T is the total time taken by a material removal process, and Y is the expected yield following a material removal process:
                    T        =                              ∑                          i              =              1                        N                    ⁢                      T            i                                              Equation        ⁢                                  ⁢        1            
                    Y        =                              ∏                          i              =              1                        N                    ⁢                      Y            i                                              Equation        ⁢                                  ⁢        2            
Numerous steps in conventional semiconductor lithography material removal processes are expensive and time consuming, and potentially introduce defects into the desired pattern, lowering yield. Process-induced defects can be introduced by, for example, wafer handling, resist spin and heating, lithography, resist development, etch, deposition, inspection, implantation, thermal processing, and chemical-mechanical polishing.